Digoxin toxicity

Background

  • Positive inotropic effect
    • Inhibits Na-K pump -> incr extracelluar K, incr intracellular Na -> incr intracellular Ca
  • Increases vagal tone
  • Decreases refractory time; increases automaticity
    • Increases risk of dysrhythmias
  • Renally cleared
  • Hemodialysis does not work
  • 1 fab vial binds 0.5mg of digoxin

Risk Factors

  • Electrolyte
    • Hypokalemia, hypomagnesemia, Hypercalcemia
  • Hypovolemia
  • Cardiac ischemia
  • Renal insufficiency
  • Hypothyroidism
  • Meds
    • CCBs, amiodarone

Work-Up

  • Dig level
    • Normal = 0.8-2 ng/mL
      • May have toxicity even with "therapeutic" levels
    • Measure serum level at least 6 hours after acute ingestion, immediately for chronic ingestion
      • If measure before this may be falsely elevated due to incomplete drug distribution
  • Chemistry
    • Hyperkalemia level correlates with degree of toxicity
      • Hyperkalemia does not cause death; lowering K+ does not reduce mortality
    • Hypokalemia increases susceptibility in chronic toxicity
    • Hypomagnesemia is common
  • Cr/BUN
  • Urine output
  • ECG (serial)

Clinical Manifestations

Cardiac

  • Any type of dysrhythmia is possible except for rapidly conducted atrial arrhythmias
  • Most common:
    • PVCs
    • Bradycardia
  • Digitalis Effect
    • T wave changes
    • QT interval shortening
    • Scooped ST segments with depression in lateral leads

GI

  • Nausea/vomiting
  • Abdominal pain

Neuro

  • Confusion
  • Weakness
  • Visual disturbances
    • yellow halos
    • Scotomas
  • Delirium

Treatment

Fab Fragment Therapy

  • Indications
    • Severe rhythm disturbances refractory to conventional therapy
    • End-organ dysfunction
    • Hyperkalemia >5 after acute overdose
    • Pacemaker (may mask cardiac dysrhythmia)
    • Consider for:
      • Dig level > 10 in acute ingestion
      • Dig level > 4 in chronic ingestion
      • If adult acutely ingests > 10mg
      • If child acutely ingests > 4mg
  • Side effects
    • Allergic reaction
    • Withdrawal of dig effect:
      • CHF, a fib w/ RVR
    • Hypokalemia
  • How To Use
    • 1. Neither amount ingested nor digoxin level are known:
      • Adult dose
        • 10 vials over 30 min
      • Peds dose
        • 5 vials over 30 min
      • Peak effect occurs after 90min, initial response after 20min
        • Repeat dose if clinical response is inadequate
    • 2. Amount ingested is known but digoxin level is unknown
    • Step 1: Calculate total body load (TBL)
      • TBL = dose (in mg) ingested
    • Step 2: Calculate number of vials needed
      • Number of vials = TBL X 2 (round up to nearest whole number)
    • 3. Steady state digoxin level is known
    • Number of vials = (dig level(in ng/mL) X pt wt) / 100
    • 4. Chronic toxicity without severe signs
    • Give half the recommended dose
      • Otherwise may unmask the condition for which the pt is taking digoxin

Activated charcoal

  • Only an adjunctive tx; NOT an alternative to fab fragment therapy
  • Consider only if present within 2 hr of ingestion
  • 1g/kg (max 50g)

Hyperkalemia

  • Do not treat! Do not give calcium!
    • Once fab is given hyperkalemia will rapidly correct
      • Aggressive tx with potassium-lowering agents could cause sig hypokalemia following therapy

Hypokalemia

  • Treat!

Hypomagnesemia

  • Treat
  • Rhythm Disturbance
    • Bradycardia (symptomatic)
      • Atropine 0.5mg IV
      • Pacing
    • Tachyarrhythmias
      • K
      • Mag
      • Lidocaine
      • Phenytoin
      • Cardioversion

Source

Rosen's, UpToDate